The proposed study is the beginning of a long-term investigation of the synaptic organization of the basolateral amygdala that will focus on the basal amygdalar nucleus (BAN). The amygdala is one of the chief forebrain regions concerned with emotion. Clinical interest in the basolateral amygdala stems from its involvement in temporal lobe epilepsy, Alzheimer's disease, and psychiatric disorders (including anxiety, depression, and schizophrenia). It is also one of the main regions targeted by benzodiazepines and other psychiatric medications. Despite the importance of this brain region, very little is known about the synaptic organization of its constituent psychiatric disorders involving the amygdala. The proposed studies will focus on the inhibitory interneurons of the BAN. These investigations will use immunocytochemical methods at the light and electron microscopic levels to identify the main subpopulations of inhibitory interneurons and to analyze their connections: 1) with the principal neurons of the BAN, 2) with the serotonergic, dopaminergic, and noradrenergic afferents to the BAN, and 3) with each other. The synaptic connections of electrophysiological characterized principal neurons and interneurons will also be examined; this represents the first time that electrophysiological and ultrastructural techniques will be combined to elucidate the synaptic organization of the basolateral amygdala. In addition, it will be determined if particular interneuronal subpopulations in the BAN exhibit specific subtypes of GABAergic, glutamatergic, and monoaminergic receptors, and whether there are extensive non-synaptic interactions of monoaminergic transmitters with BAN neurons.III.